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Appendix A - Historical Background River City Petroleum and Connell Motor Lift Truck Page 12 of 14 • The aerial extent of the soil contamination in the vadose zone is defined DISTRIBUTION OF TPH-G AND BTEX - FORMER UST AREA • A release of petroleum hydrocarbons(TPH-g, TPH-d)and benzene, toluene, ethylbenzene and xylene (BTEX) compounds occurred from dispenser line releases • Petroleum hydrocarbons were not detected in the soil samples collected from below the former UST area, nor excavation, however the most significant mass of hydrocarbons are found below the UST area proper Available data is suggestive of a release that was most severe at the southern most dispenser islands, less at the north dispensers and even less between the dispenser islands Once released TPH/BTEX to the subsurface, the contaminants migrated north under the former UST area then to a vertical depth of approximately 55 feet bsg near the current water table, where the variation concentration in soil samples suggest a smear zone between 50 feet and 60 feet bsg At this point the TPH contaminants migrated locally down to a depth of 75 feet bsg, where non-detect soil samples were collected at the former UST area Additionally, minor concentrations of 1,2-DCA were detected in soil samples collected at the depths of 65 feet to 85 feet bsg, collected below the former UST area • The highest TPH-g and BTEX impact to soil in the upper vadose zone is present at monitoring well borings throughout the former UST area The TPH-g highest impact to soil near the water table and below the water table to a depth of 75 feet bsg occurs in the UST area A smear zone of five feet of saturated soil contamination is documented at the wells east of the dispenser area, west under the building, where the smear zone of saturated, impacted-soil expands to ten or fifteen feet in thickness The aerial extent of the soil contamination in the vadose zone is defined to the west of the former UST area • TPH-g and BTEX compounds were detected in ground water samples collected directly west of the dispenser island at maximum concentrations of 197,000 gg/l and 18,000 gg/1 (benzene) Relatively significant concentrations of TPH-g and BTEX compounds were detected in ground water samples collected directly east of the former dispenser island, in the shallow ground water and towards the west under the building at the site • TPH-g and BTEX compounds were also detected in deeper ground water samples collected from wells within the building on the site and each of the deep CPT samples near well MW-1, inexplicably increasing or remaining at stable concentrations with depth, and migrating towards the west from the former UST area • The vertical and the lateral extent of TPH and BTEX previously had been defined by monitoring well samples collected at MW-34 However, a deep CPT grab-sample collected from beneath the former dispenser area leak, indicated dissolved contamination and the Advanced GeoEnvironmental,Inc